This invention relates to medical imaging systems having high speed multiple-wire cables.
Remote imaging systems are used to view objects not normally accessible to human observation or conventional optical imaging tools. Only limited-size image transducers are positioned for viewing, and a signal is transmitted to a remote location for viewing. For instance, surgeons use optical imaging probes to view internal anatomy for diagnosis or surgery. Such systems require miniaturized multi-wire cable assemblies to transmit image signals recorded by a charge coupled device (CCD) to an external display screen. Other medical imaging systems use an ultrasound transducer that contacts the patient externally, to transmit an internal image via a multi-wire cable to an instrument for display.
For surgical and other applications, it is desirable to minimize the cable size. Limited diameter facilitates desired flexibility. However, a detailed real-time image needs significant bandwidth, requiring many separate conductors of a given frequency capability. To avoid undesirably bulky cables when substantial numbers of conductors are required, very fine conductors are used. To limit electrical noise and interference at high signal frequencies, conductors are generally shielded. A typical approach employs fine coaxial wires, which are bundled in a cable. Each wire includes its own shield, which provides suitable protection against interference at high frequencies.
While adequate, multiple coaxial assemblies have several disadvantages. The manufacturing cost of fine coaxial wiring is higher than is acceptable for many applications. The mode of terminating very fine coaxial wire is complex and expensive. And coaxial wires generate unwanted bulk due to the need for a given spacing between core conductor and shield.
The present invention overcomes the limitations of the prior art by providing a medical imaging system with a base unit including an electronic display, and a remote imaging transducer connected to the display unit via a flexible cable. The cable includes a number of signal transmission lines, each of which includes a twisted pair of conductors used for digital differential signaling. These twisted pairs maintain signal integrity without a shield by utilizing the well known advantages of differential signals, namely the elimination of signal radiation and the reduction of common mode interference. Digital systems utilizing differential signaling include LVDS, SCI, Fiber Channel, and Firewire. Each conductor is connected at a first end to the transducer, and at a second end to the base unit. The signal transmission lines may be wrapped about a core, which may be an optical conduit communicating with a light source at the base unit. The system may employ optical or ultrasound imaging.